Blood pressure increases with age, and over time, in some individuals, reaches proportions consisent with clinically defined hypertension. The age-dependent increase in blood pressure starts in mid-childhood and accelerates during puberty and in the post-pubertal period. Thus, mechanisms for the development of hypertension are likely present at an early age. Hypertension may be produced by an interplay of sodium retention and adrenergic pressor effects. In the present study, production of aldosterone (the major sodium retaining hormone) and the activity of the sympathetic nervous system (norepinephrine) will be examined in a mixed-longitudinal design in white and black boys and girls beginning at ages 6 to 12 and extending to age 17. Levels of these pressor systems will be determined in the basal state from measurements made in urine samples collected overnight (sleep urine). To enhance the likelihood that school children will comply with the multiple observations required for this longitudinal study, measurements will be deliberately restricted to non-invasive ones. Specifically, aldosterone and norepinephrine excretion measured in sleep urine (their rates adjusted for dietary intake of sodium and potassium as reflected in electrolyte urinary excretion) will be obtained at 6 month intervals in addition to blood pressure, heart rate, weight, height, and skin-fold thickness. In addition, family history of hypertension and parental blood pressures will be used as covariates in analysis of data in children. A second aspect of this study concerns the observation that blood pressure increases at a faster rate during adrenarche (a period of increasing adrenal androgen production) and puberty. Androgens produced during periods of adrenal and gonadal maturation may contribute to the increase in blood pressure in the relationship of androgens to blood pressure will be examined by distinguishing blood pressure responses to androgen production from effects of androgens on physical growth, thus exploring the concept that androgens interact directly with pressor systems to raise blood pressure. Levels of androgen production during the adrenarche will be determined by measurement of dehydroepiandrosterone-sulfate excretion, and during puberty by measurement of luteinizing hormone excretion, in sleep urine samples. In summary, this study will be the first longitudinal study correlating changes in pressor substances with blood pressure during growth and sexual development in which biological indices of maturation will be employed.